Fusarium verticillioides GBB1, a gene encoding heterotrimeric G protein β subunit, is associated with fumonisin B1 biosynthesis and hyphal development but not with fungal virulence

Abstract

Fusarium verticillioides (Sacc.) Nirenberg (teleomorph Gibberella moniliformis Wineland) is a maize pathogen that causes ear rots and stalk rots. The fungus also produces a group of mycotoxins, fumonisins, on infected ears, which cause considerable health and economic concerns for humans and animals worldwide. To date, our understanding of the molecular mechanisms associated with fungal virulence and fumonisin biosynthesis in F. verticillioides is limited. In this study, GBB1, a gene encoding a putative β subunit of a heterotrimeric G protein, was disrupted and the effects on fumonisin biosynthesis and virulence were evaluated. A GBB1 deletion mutant (Δgbb1) showed no significant differences in radial growth and mycelial mass but produced significantly less fumonisin B1(FB1) than its wild-type progenitor. HPLC analysis showed that Δgbb1 produced less than 10 p.p.m. FB1 while the wild-type produced over 140 p.p.m. when strains were grown on cracked corn kernels. Reduced expression of the key FB1 biosynthetic genes, FUM1 and FUM8, in Δgbb1 provides further evidence that GBB1 is involved in FB1 regulation. Stalk rot virulence, as measured by mean lesion length and by area, was not significantly different in Δgbb1 compared with the wild-type, suggesting that GBB1 does not regulate virulence in F. verticillioides. Developmentally, hyphae of Δgbb1 do not deviate from the original axis of polarity established upon germ tube emergence in contrast to wild-type hyphae that meander on and off axis as they grow. Complementation of Δgbb1 with GBB1 restored FB1 production and hyphal growth to wild-type. The results of this study demonstrate that heterotrimeric G protein β subunit plays an important role in regulation of FB1 biosynthesis and hyphal growth, but not virulence in F. verticillioides. © 2007 Blackwell Publishing Ltd.